Effect

Generation I

If the last amount of damage done before the use of Counter is greater than 0 and was dealt by a Normal-type or Fighting-type attack, Counter will do twice as much damage to the opponent. Although Counter deals Fighting-type damage, its type does not alter the amount of damage it inflicts. Counter works against Ghost types, although they are immune to Fighting-type attacks.

Counter is a decreased priority move. If the opponent does not use a decreased priority move during the round that it is used, Counter will go last regardless of the user's or opponent's speed. If the opponent also uses a decreased priority move during the same round, the attack order of the users will be determined normally. If the user is put to sleep or is frozen during the round that Counter is (or attempts to be) used, Counter's decreased speed priority will not be reset. Subsequently, it will only be reset on the turn after the user wakes up or is defrosted, or if the user switches out.

Counter can cause a critical hit, but the actual amount of damage dealt by it will not be altered by a critical hit. Counter will only counter the last hit of a multi-hit move and the last attack of a partial trapping move. Counter will always miss if called by Metronome.

Switching, full paralysis, and using a multi-turn move will not reset the last amount of damage done, allowing Counter to counter itself as well as self-inflicted recoil damage. However, if both active Pokémon use Counter during the same round, both attacks will fail. An attack absorbed by a substitute can be countered for the amount of damage it would have done to the user had the user not had a substitute.

If an HP-restoring item is used on the opponent during the same round that Counter is used, Counter will counter the item.

In Stadium, switching, full paralysis, and using a multi-turn move reset the last amount of damage done, so Counter can't counter itself or self-inflicted recoil damage if the opponent does not make a move on its following turn.

Generation II

Counter counters all physical moves for twice the damage done to the user. Counter no longer counters a move that hits a substitute. Furthermore, Ghost-type Pokémon are now immune to Counter.

Generation III-IV

In Double Battles, Counter will hit the last opponent that dealt physical damage to the attacker. Counter cannot affect allied Pokémon.

Generation V

In Triple Battles, Counter can hit non-adjacent opponents provided a non-adjacent opponent was the last Pokémon to attack the user.

If the Pokémon using Counter is hit by a Physical attack that deals 0 damage, Counter becomes a Physical move with 1 Base Power.

In side games

In Super Smash Bros. Brawl, Counter is Lucario's down Special move. When Lucario uses Counter, it prepares to counterattack. If hit while preparing, Lucario will disappear and reappear behind the opponent, attacking them.

Trivia

In the Spanish versions of the games, the move is called Contador (someone or something that counts - a counter). However, in the animedub, the move is properly translated as Contraataque (counterattack).